Estimated A1C (eA1C)
Also called estimated HbA1c.
Estimated A1C converts a mean glucose from CGM or fingersticks into a value on the A1C scale. In 2018 a panel renamed it the glucose management indicator (GMI) with an updated formula, so the result would not be read as a lab A1C. The related ADAG study runs the other way: it turns a lab A1C into an estimated average glucose (eAG). (Bergenstal et al., GMI, 2018)
Formula
ADAG regression: estimated average glucose (mg/dL) = 28.7 × A1C − 46.7, or (mmol/L) = 1.59 × A1C − 2.59. Solved for A1C: A1C = (mean glucose in mg/dL + 46.7) ÷ 28.7.
(Nathan et al., the ADAG study, 2008)
Worked example
A mean glucose of 154 mg/dL (8.5 mmol/L): (154 + 46.7) ÷ 28.7 = 7.0%. GMI for the same mean is also 7.0%; the two formulas drift apart at higher means (250 mg/dL gives 10.3% here and 9.3% as GMI).
Related terms
Sources, quoted
- Bergenstal et al., GMI, 2018: “Estimated A1C (eA1C) is a measure converting the mean glucose from CGM or self-monitored blood glucose readings, using a formula derived from glucose readings from a population of individuals, into an estimate of a simultaneously measured laboratory A1C.”
- Bergenstal et al., GMI, 2018: “It was suggested that the new term not include either “estimated” or “A1C” to avoid a misinterpretation that the value of this metric should always closely match a corresponding laboratory-measured A1C.”
- Nathan et al., the ADAG study, 2008: “allowing calculation of an estimated average glucose (eAG) for A1C values.”
- Nathan et al., the ADAG study, 2008: “*Linear regression eAG (mg/dl)=28.7 × A1C − 46.7.”
Every quote above is checked against its source page before each update of this site; last checked 2026-10-06. The worked example is our own arithmetic. This page explains a term; it is not advice for a person's treatment.